Wireless devices can transfer data via infrared communication ports or with radiofrequency (RF) data transfer. Microwave technologies such as Bluetooth and WiFi allow non-line-of-sight device-to-device communication. However, due to security concerns, these technologies require a set-up process in which a device must be added to the network. Although near-field-communication (NFC) can be used to exchange data between devices without adding a device to network, it functions only at a distance of ten centimeters or less.
Modern wireless devices have a large range and therefore may be in contact with many other wireless devices at any particular time. Thus, if a device is seeking to transfer data to or from another device, it may have a large number of devices from which to select the desired wireless device. Additionally, there is the possibility that another device within range may interfere with, or breach the security of, a particular wireless device. To minimize the potential for a security breach, one method of exchanging data is synchronization of the interaction, in which the users of two or more devices press a button to open a small security hole for a short window of time and exchange security keys. Some existing mobile devices can exchange accelerometer signals recorded when users bump their phones together. The exchange of accelerometer signals allows the devices to then exchange information.